Introduction: The Improved Chopping Machine


Behold, the second functioning prototype of The Chopping Machine. If you have not seen my previous prototype, I suggest you check it out on my profile. It's pretty cool.

The Chopping Machine project is something I am working on for my studies in industrial design at Emily Carr University. I made this under the guise of critical design. Critical design is not easy to explain in a sentence or two, so I suggest you look it up for full context of this project. This machine is an illustration of our ever growing reliance on technology, and how we are constantly inventing things to do things for us that we could have done better ourselves by hand. However, this is one of the ways that life changing things are invented, by inventing things that we did not even know we needed. This may not be one of those things, but who knows maybe we do need a machine something like this in every kitchen.

One of the biggest differences from the old machine is that all the cardboard has been replaced by wood. Also, I replaced the previous shaft-motor connection solution with an actual motor coupling. Instead of the 3-way switch that I used for an activation button on the old model, I used an arcade button which provides momentary-on activation. I will go over the other changes I made as the tutorial progresses.

In this Instructable I will show you how to make this machine just as I did!

Step 1: Things You Will Need


  1. Cleaver
  2. DC motor with high torque capabilities
  3. Chopping board
  4. Momentary-on button or switch
  5. Access to a (working) 3D printer
  6. Hemlock 2x4's, 10 ft
  7. Wire, shrink wrap
  8. Matching AC power adapter and jack (hobby electronics store)
  9. 1/4" metal rod
  10. 4 x 1/4" pillow blocks (McMaster Carr for source)
  11. Nails
  12. Wood glue
  13. Wood screws
  14. 1/4" dowels
  15. 4 x 1/4" universal set screw mounting hubs (sparkfun for source)
  16. 12mm - 1/4" set screw shaft coupler (McMaster Carr for source)

  17. 4 x 1/4" pillow blocks (McMaster Carr for source)

Step 2: More Things You Will Need


  1. Access to a wood shop
    • Drill press
    • Radial arm saw
    • Milling machine
    • Band saw
    • Table saw
    • Belt sander
    • Disc sander
  2. Hand tools
    • Hacksaw
    • Sanding block/sandpaper
    • File/rasp
    • Lots of clamps (at least 4 big ones)
    • Battery powered drill
    • Drill bits up to 1 1/8" down to 1/8"
    • Pliers
    • Soldering kit
    • Allen keys
    • Wood filler (for mistakes)
    • Paint scraper

Step 3: Assess Changes to Make and Order Parts

Shortly after demonstrating my first (cardboard) prototype, it broke. Predictably, the cam shaft and the motor connection was not strong enough, causing the motor twisting free of the cam shaft. After all, it was merely held in place with electric tape.

Taking apart the original machine was challenging. By gluing parts in, removing the motor became difficult. I had no where to fit the screwdriver to unscrew it. Removing the cam shaft was also difficult, the cams would collide with the knife pivot struts as I tried to remove it.

To solve this I designed the parts of the new prototype to be removable.

The cutting board also got a little gross after cutting a few random things, so the cutting board became removable too.

Order specialty parts ahead of time such as the activation switch, universal set screw mounting hubs, pillow blocks, and shaft coupler. The parts will be needed to conduct test fitting and measurement as construction progresses. For this prototype I used set screw parts because of their low profile and ease of assembly.

Step 4: Sketch Up New Version, and 3D Print Cams

Sketch up designs with the changes you wish to make. It is a good idea to let whoever is operating the CNC and 3D printer know that you want to have something made with the tool, so you can get the parts done in time. Initially I intended to CNC the base out of hemlock, but my plans fell through ultimately. With my basic knowledge of 3D modeling, I attempted to sketch my ideas for a new base in Fusion360, so I could CNC the base. Fusion 360 is a 3D modeling software that also doubles as CAD and 3D printing file generators. I sketched out other ideas on paper. Consider dimensions and spacing of parts in the sketches.

I played with the idea of fixing the cutting board into the base by cutting a dovetail fitting into the base and board. Cutting a pocket for the cutting board to sit in was another idea that crossed my mind. I opted for neither, because those ideas required extensive and precise milling of a large area. If I attempted to mill such a feature into the board, the surface would be uneven and not precise. Instead I left the surface of the base as it was, because it was already flat and I did not need to raise or lower the cutting board.

I modeled new cams in Fusion360 traced off a photo of the old cam. I printed 3 different versions of the cam, two of them based off of the spiral tool in Adobe Illustrator. I expected I would be able to test different shapes of cams on this prototype, but when screwing the universal hubs and cams together on the cam shaft, the screws broke. The screws broke due to excessive torquing while not fully screwed in. Inaccuracy while drilling through the cam is likely the culprit, although the cam shaft could have been bent too.

Step 5: Make the Base!

Prepare Wood for Lamination

I started with a 8 foot 2x4 of hemlock, inspected for cracks and other damage. Always start with more than you need.

Process the board through the radial arm saw, jointer, and planer to end up with square edges and equal thickness.


Glue and clamp, let set overnight as per wood glue instructions. You can never have too many clamps, so be excessive. As I learned through this process, there are two different types of clamps you need to use to laminate edges together. You need bar clamps and C clamps. The bar clamps will hold pressure to the edges, and the C clamps will hold pressure to keep the boards flat. A tool called a caul is utilized with the C clamps to keep the edges flat and parallel,which is really just a 1x2 that has packing tape on on side. The side with the packing tape is flat, so when sandwiched between 2 cauls, the end lamination is nice and flat.

I had to glue the boards in two steps, two by two. In total the glue was all set in two days. Plan accordingly.

Prepare Board for Milling

After the glue is set, un-clamp and scrape excess glue off with a paint scraper. Table saw the unaligned ends off to size, and sand with a palm sander until flat and glue residue is gone. Sand edges until free of machine marks.

Step 6: Make Struts and Mill Electric Channel

Making Struts

Attention must be paid to the height of the knife pivot struts and the cam shaft struts. Consider the height of the pillow block under the axis. I referenced the height needed directly from the previous cardboard version, since the machine functioned well.

Before screwing the pillow blocks onto the struts, pre drill holes for 2 1/4" pegs, and holes for screws to affix the pillow block. Perform drilling on a drill press if possible, and for best results go slow and remove small amounts of material at a time.

Milling the Base

Part of my original CNC'd idea was for the bottom to have a channel cut on the underside to conceal wiring. Instead of using a computer controlled mill, I used a more traditional wheel cranked milling machine.

Still being relatively new to woodworking and milling, I hogged out a deep channel to make room for the button and the power jack. Go slowly, the wood will have a cleaner cut. Always double check you know which way the table moves before cutting.

I acquired my button late in the process so I did not make the base board thick enough to house the button sufficiently. I had to raise the board off the underside of the activation button, with less-than-optimal cardboard feet. I will replace the cardboard with felt spacers soon.

Step 7: Drill All the Holes

As per my design, you will need holes in the base for the:

  • cutting board
  • motor mount
  • cam shaft struts
  • knife pivot struts
  • activation button
  • motor wiring

And holes in the cam and knife struts for:

  • pillow block screws
  • 1/4" dowels

A drill press is the best tool for this application. At this step you will drill holes for the motor wiring, activation switch, and dowels. I fixed all of the components to the base with 1/4" dowels, so they could be removed for cleaning. The cutting board is held by only two dowels, despite drilling holes for each corner. The board is removed frequently and is easier to remove when only held by two dowels.

Measure the distance between an edge of the base and the placement of each component, and mark accurately on the base. Center punch each hole and pre drill the holes with small drill bit sizes in order to achieve a straight and accurate hole. Drill at a slow and steady rate to minimize blowout of the wood. Be sure to liberally clamp the work to the table to ensure a safe and accurate drill job. Unfortunately I did not have access to a drill press when I needed to drill holes for dowels, so they were a bit off-center. This led to my struts not lining up very well on the base. For the cutting board I used paint to mark the position of the dowels on the cutting board. It was not a very accurate method but fit surprisingly well.

Step 8: Make Motor Mount

Depending on what shape of motor you end up with, your motor mount may or may not end up looking like mine.

My motor has four screw holes which can fix a 1/4" sheet of something between it. I chose baltic birch 1/4" plywood, because of its strength. I created an "L" shape out of more plywood, glued together and fixed via screws to the piece between the motor. For clarification, refer to the pictures above.

Cut the plywood the height of the motor plus its space off the base, and as wide as the motor. Drill a hole large enough for the motor shaft to stick through, and holes for screws to mount the motor to the bracket.

Make a block planed thin enough stick between the motor and the base, but thick enough to screw together. Although I used plywood for the bottom of the mounting bracket, I would have used hemlock.

Drill holes into the motor mount and base for 1/4" dowels to fix the bracket in place in at least 3 places.

Step 9: Make Cam Shaft and Drill Holes in Cams

Cut Metal Rod

Assemble motor to the motor mounting bracket, and affix the cam shaft coupler to the the motor. Measure accurately a length of 1/4" metal rod (preferably a hard metal such as steel), and cut with a hacksaw accurately. Metal is hard to manually trim so a well placed cut is vital to optimal fitment. Sand the ends to eliminate burrs and test fit with pillow blocks and universal mounting hubs. If you do not have a pivot pin for the end of the knife, cut a section off for it.

File Flat Sections

To make flat sections on the cam shaft for the set screws to lock into, assemble the cams and universal mounting hubs to the cam shaft. Place the knife struts in their mark and adjust the cams so they make room for the struts. Mark the borders of the areas which the parts occupy on the cam shaft. Remove the parts and clamp the metal rod in a vice. Use a hand file to grind the marked areas flat. Do not remove more than a third of the diameter of the rod or you will compromise structural integrity.

Once you have marked the areas where the cams will reside, measure off a section of metal rod for the cam pin. Leave some extra length so the cam pin spans past the tops of the cams.

Drill Cam Mounting Holes

After making the cam shaft, this is the best point to drill holes in the cams. The metal rod may be bent or the flat spots on the shaft may not be parallel. Assemble the cams in their appropriate position and mark, with a mechanical pencil or preferably some sort of center punch, the holes in the universal mounting hub. Once marked, remove the mounting hubs and cams from the cam shaft, and proceed to drill holes for the hub screws.
Again a drill press is the best tool for this job.

Step 10: Make Plug Plate and Solder

Make Mounting Plate for Plug

I moved the power adapter plug from the top of the machine to the top left corner on the edge. The charging port on a Macbook is on the top left corner on the edge as well, so users of this machine will likely know where to look for the power plug.

The way this plug mounts into wood is by a small, threaded ring that tightens on material between it and the body of the plug. I cut a section of plywood that fit the indent i milled on the base, and drilled a hole for the power plug to fit through. The plug was longer than the piece of plywood was thick, so I added an extra layer behind it. I nailed the piece into the side of the base to fix it in place.

Solder and Assemble

Thread the motor wires through the surface of the base, and solder the circuit as the drawn diagram indicates. If the motor is spinning the cam shaft the wrong way, you will have to undo the soldering and flip the positive and negative wires coming from the motor. Don't forget to place heat shrink on your wires before soldering, and tin your contacts fully.

Step 11: FINISHED!

After soldering, the device is done. Assemble the parts, plug in the power, and you are ready to rock on some vegetables! Or whatever you want to chop! Just hold down the activation button and let her rip!

This was an extremely fun project to work on and I would like to thank my instructors Dr. Garnet Hertz and Bobbi for making this project possible, as well as the shop techs who without their help, this project would have been completed years from now.

Woodworking Contest 2017

Runner Up in the
Woodworking Contest 2017

Robotics Contest 2017

Participated in the
Robotics Contest 2017